Conventional flipchip contacts can be surface mounted in a relatively uncritical fashion as long as they are soldered as soldering globules on contact surfaces of semiconductor chips. Reliability problems do not occur until electrodeposited bases with external contacts are used as flipchip contacts. Even pretreatment by wet etching does not yield the desired improvement in the surface mounting reliability, as achieved with soldered-on flipchip contacts as soldering globules. Rather, it is to be stated that wet etching of distinct bases with external contacts increases the roughness of the base surface, the result being a jagged base surface.
Nevertheless, the need exists to replace the conventional soldering globules for flipchip contacts by electrodeposited bases with external contacts, since the operation of mounting soldering globules on semiconductor chips or on semiconductor wafers is a critical process that, solely by the distribution of the many soldering globules on a semiconductor wafer in predetermined positions, specifically the contact surfaces of the semiconductor wafer, is a time-consuming and critical one, whereas the electrodeposition of bases with external contacts on a semiconductor wafer can be carried out in a time-saving fashion by means of appropriate masking techniques for a multiplicity of bases with external contacts and, at the same time, for a multiplicity of semiconductor wafers, by contrast with soldering globules for which each semiconductor wafer on each semiconductor chip has to be provided individually with soldering globules. This requires complicated distribution and adjustment techniques for the flipchip contact soldering globules.
The reliability problems in electrodeposited bases with external contacts are to be ascribed in part to contaminants in the electrodeposited materials. The problems also are based in part on hydrogen spraying of the metal mixtures of the electrodeposited bases with external contacts. Such defects and contaminations which depress the surface mounting reliability of contact bases, can be caused by the most varied additives that are added to the metal salts of an electrodeposition bath in order to increase the wettability or the flowability of the electrodeposition bath. Thus, brighteners, wetting agents, cyanides or other organic substances such as citric acid, are added, for example in order to minimize precipitation reaction products. Such problem substances are not included in soldering globules since they arise from melting in a spraying or dripping process and do not come into contact with liquids such as electrodeposition baths.